The present invention relates to a flexible fluid containment vessel (sometimes hereinafter referred to as xe2x80x9cFFCVxe2x80x9d) for transporting and containing a large volume of fluid, particularly fluid having a density less than that of salt water, more particularly, fresh water, and a method of making the same.
The use of flexible containers for the containment and transportation of cargo, particularly fluid or liquid cargo, is known. It is well known to use containers to transport fluids in water, particularly, salt water.
If the cargo is fluid or a fluidized solid that has a density less than salt water, there is no need to use rigid bulk barges, tankers or containment vessels. Rather, flexible containment vessels may be used and towed or pushed from one location to another. Such flexible vessels have obvious advantages over rigid vessels. Moreover, flexible vessels, if constructed appropriately, allow themselves to be rolled up or folded after the cargo has been removed and stored for a return trip.
Throughout the world there are many areas which are in critical need of fresh water. Fresh water is such a commodity that harvesting of the ice cap and icebergs is rapidly emerging as a large business. However, wherever the fresh water is obtained, economical transportation thereof to the intended destination is a concern.
For example, currently an icecap harvester intends to use tankers having 150,000 ton capacity to transport fresh water. Obviously, this involves, not only the cost in using such a transport vehicle, but the added expense of its return trip, unloaded, to pick up fresh cargo. Flexible container vessels, when emptied can be collapsed and stored on, for example, the tugboat that pulled it to the unloading point, reducing the expense in this regard.
Even with such an advantage, economy dictates that the volume being transported in the flexible container vessel be sufficient to overcome the expense of transportation. Accordingly, larger and larger flexible containers are being developed. However, technical problems with regard to such containers persist even though developments over the years have occurred. In this regard, improvements in flexible containment vessels or barges have been taught in U.S. Pat. Nos. 2,997,973; 2,998,973; 3,001,501; 3,056,373; and 3,167,103. The intended uses for flexible containment vessels is usually for transporting or storing liquids or fluidisable solids which have a specific gravity less than that of salt water.
The density of salt water as compared to the density of the liquid or fluidisable solids reflects the fact that the cargo provides buoyancy for the flexible transport bag when a partially or completely filled bag is placed and towed in salt water. This buoyancy of the cargo provides flotation for the container and facilitates the shipment of the cargo from one seaport to another.
In U.S. Pat. No. 2,997,973, there is disclosed a vessel comprising a closed tube of flexible material, such as a natural or synthetic rubber impregnated fabric, which has a streamlined nose adapted to be connected to towing means, and one or more pipes communicating with the interior of the vessel such as to permit filling and emptying of the vessel. The buoyancy is supplied by the liquid contents of the vessel and its shape depends on the degree to which it is filled. This patent goes on to suggest that the flexible transport bag can be made from a single fabric woven as a tube. It does not teach, however, how this would be accomplished with a tube of such magnitude. Apparently, such a structure would deal with the problem of seams. Seams are commonly found in commercial flexible transport bags, since the bags are typically made in a patch work manner with stitching or other means of connecting the patches of water proof material together. See e.g. U.S. Pat. No. 3,779,196. Seams are, however, known to be a source of bag failure when the bag is repeatedly subjected to high loads. Seam failure can obviously be avoided in a seamless structure. However, a seamed structure is an alternative to a simple woven fabric as it would have different advantages thereto, particularly in the fabrication thereof.
In this regard, U.S. Pat. No. 5,360,656 entitled xe2x80x9cPress Felt and Method of Manufacturexe2x80x9d, which issued Nov. 1, 1994 and is commonly assigned, the disclosure of which is incorporated by reference herein, discloses a base fabric of a press felt that is fabricated from spirally wound fabric strips.
The length of fabric will be determined by the length of each spiral turn of the fabric strip of yarn material and its width determined by the number of spiral turns.
An edge joint can be achieved, e.g. by sewing, melting, and welding (for instance, ultrasonic welding as set forth in U.S. Pat. No. 5,713,399 entitled xe2x80x9cUltrasonic Seaming of Abutting Strips for Paper Machine Clothingxe2x80x9d which issued Feb. 3, 1998 and is commonly assigned, the disclosure of which is incorporated herein by reference) of non-woven material or of non-woven material with melting fibers.
While that patent relates to creating a base fabric for a press felt such technology may have application in creating a sufficiently strong tubular structure for a transport container. Moreover, with the intended use being a transport container, rather than a press fabric where a smooth transition between fabric strips is desired, this is not a particular concern and different joining methods (overlapping and sewing, bonding, stapling, etc.) are possible. Other types of joining may be apparent to one skilled in the art.
Furthermore, while as aforenoted, a seamless flexible container is desirable and has been mentioned in the prior art, the means for manufacturing such a structure has its difficulties. Heretofore, as noted, large flexible containers were typically made in smaller sections which were sewn or bonded together. These sections had to be water impermeable. Typically such sections, if not made of an impermeable material, could readily be provided with such a coating prior to being installed. The coating could be applied by conventional means such as spraying or dip coating.
Another problem is how to seal the end of the container especially where there is tapering at the end desired. While end portions can be made separately and attached to the tubular structure, examples of which are set forth in the aforesaid applications and the references cited therein, it may be desirable to have the end portions formed out of the tubular structure itself and formed into a desired shape (i.e. cone shaped etc.). In this regard, for example, U.S. Pat. No. 2,997,973 issued on Aug. 29, 1961 to Hawthorne shows the use of pleating of the fabric at the ends which are then glued and/or sewn to provide the desired shape.
Accordingly, there exists a need for a FFCV for transporting large volumes of fluid which overcomes the aforenoted problems attendant to such a structure and the environment in which it is to operate.
It is therefore a principal object of the invention to provide for a relatively large fabric FFCV for the transportation of cargo, including, particularly, fresh water, having a density less than that of salt water.
It is a further object of the invention to provide for such an FFCV which has means of sealing the ends thereof in a desired manner.
It is a further object of the invention to provide means for sealing the ends of such an FFCV by tapering.
A further object of the invention is to provide for a means for sealing the ends of such an FFCV so as to effectively distribute the load thereon.
These and other objects and advantages will be realized by the present invention. In this regard the present invention envisions the use of a woven or spirally formed tube to create the FFCV, having a length of 300xe2x80x2 or more and a diameter of 40xe2x80x2 or more. Such a large structure can be fabricated on machines that make papermaker""s clothing. The ends of the tube, sometimes referred to as the nose and tail, or bow and stern, may be sealed by a number of means, including being pleated, folded or otherwise reduced in diameter and bonded, stitched, stapled or maintained by a mechanical coupling. More particularly, while the aforesaid patent applications disclose end portions which may be affixed to the tube or spirally formed, the present invention is directed towards making the end portions out of the tube itself. In the case of a tube formed having a large uniform circumference of perhaps 40 to 75 meters or more, it would be necessary to reduce the circumference down so as to allow an end cap or tow member to be affixed thereto. While doing so, it is desired to shape the end portion such as that of a cone or the bow of a ship, while maintaining a unitized construction. Several methods for doing this in a spiral formed FFCV are disclosed in the first aforesaid patent application. Alternative methods are disclosed hereinwith.
Several methods are envisioned whilst bearing in mind the desire to avoid stress concentrations. The first method involves folding over and pleating the ends of the tube. The pleats extend over the length of the end portion of the tube with the degree of overlapping increasing as it approaches the end so that the desired mechanical coupling can be affixed. Such graduations of the pleating allows for a smooth transition and for cones to be formed in both the front and rear. The pleats can also be folds of fabric folded upon themselves in stacks or in groups. The pleats may also extend over the entire length of the tube which, with the exception of the ends, will expand upon filling the tube. An appropriate means for securing the pleats in place is provided.
A second method involves the shaping of the bow into a desired taper by folding the tube along focal points which gradually increases the degree of the fold and then securing the end about fold facilitators and securing it. An appropriate tow bar may be attached at the nose.
A third method involves a sprocket or tooth type arrangement at the end of the tube so as to reduce its circumference. In this regard, the fabric has folded portions that extend radially upward perpendicular to the circumference of the tube. The degree of the fold increases from a minimum to a maximum at which point a mechanical end closure device is affixed.
A fourth method involves radial folds of fabric in a star shaped pattern mechanically fixed in place about the end circumference of the tube.
A fifth method involves the creation of a taper at the end of the tube during the weaving, braiding or knitting process of creating the tube. For example, in the tubular weaving process, a taper can be created by removing or eliminating warp yarns in a sequential fashion and tying them off.
A sixth method involves gathering the fabric at the end of the tube about a mandrel, folding it back and mechanically securing it.
In all cases, of course, an opening or openings are provided for filling and emptying the cargo such as those disclosed in U.S. Pat. Nos. 3,067,712 and 3,224,403.